Renal Control of Changes in the Compliance of the Interstitial Space: A Factor in the Aetiology of Renoprival Hypertension

Abstract

S U M M A R Y1. Measurements of plasma volume, haematocrit, extracellular fluid volume, blood pressure, venous pressure and interstitial tissue pressure were made in rats 4 days after unilateral nephrectomy. Measurements were repeated either 4 days after subsequent removal of the remaining kidney, or 4 days after anastomosis of the remaining ureter with the inferior vena cava. Extracellular fluid volume was expanded by giving 0.5% saline by mouth: in one series blood volume was expanded by injections of blood.2. Plasma volume (PV) rose more after bilateral nephrectomy (BN), extracellular fluid volume (ECFV) more after unilateral nephrectomy and ureterocaval anastomosis (UNUCA). The PV/ECFV ratio was significantly higher after BN.3. Blood pressure and venous pressure rose after BN but not after UNUCA. Interstitial tissue pressure (TP) rose more after BN in spite of greater expansion of interstitial fluid volume (IFV = ECFV-PV) after UNUCA. The ratio AIFV/ATP was several times less after BN than after UNUCA. 4. Interstitial space compliance was estimated by measuring changes in IFV and TP 10 min after a saline infusion (compliance = AIFV/ATP). After UNUCA there was little change from values obtained after unilateral nephrectomy alone ; following BN compliance fell severalfold.5. It is suggested that changes in compliance of the interstitial space may be brought about by a substance secreted by the kidney and represent a hitherto undetected mechanism by which plasma volume is maintained constant under different conditions of hydration. Changes in interstitial space compliance may also play a part in the aetiology of renoprival hypertension by raising tissue pressure, and thus venous pressure and cardiac output.

Whole-body venous capacity and effective total tissue compliance in SHR.

“…29 '" Our values for IFP, which ranged from +0.3 to -2.8 mm Hg and averaged -1.5 mm Hg in all rats included in this study, were slightly higher (less negative) than that (-2.5 mm Hg) reported by others using the capsule technique in rats. 11 ' M However, measurements in the present study were made in conscious rats from capsules implanted subcutaneously in the dorsal shoulder area, whereas in the previous studies, measurements were made in anesthetized rats from capsules implanted subcutaneously in the groin" or thigh 11 areas. These differences in technique might be responsible for the small difference in the results between the present and the previous studies.…”

“…They suggested that increased tone of the capacitance vessels of the clipped rats was responsible for the fluid shift. Later, Lucas and Floyer 11 '" reported evidence of decreased interstitial compliance in experimental hypertension; and Floyer 1 ' suggested that a primary fall in the interstitial compliance could be the mechanism responsible for these and many Downloaded from http://ahajournals.org by on April 2, 2019 other of their observations. It was postulated that a combination of renal fluid retention and decreased interstitial compliance might together lead to hypertension despite a normal extracellular fluid volume."…”

A Single Initiating Cause of Hypertension; Potential for Primary Prevention

“…Following a long line of investigations Floyer et al concluded that an unidentified substance released from the kidney maintains normal tissue compliance in renal as well as extra renal tissues [17]. The present hypothesis proposes that this substance is EGF.…”

Comparable effect of isotonic infusions on blood pressure in the anephric rat.

“…18 In another study, subtotal nephrectomy resulted in hypertension, 19 the incidence of which was increased in rats given saline, but the level of hypertension was similar to those not given saline. 19 The studies of Lucas and Floyer 15 and Pelling and Ledingham 20 have shown that nephrectomized rats chronically receiving either 0.5% or 1% saline as drinking water become hypertensive over a period of several days. However, in the Pelling and Ledingham study, 20 allowing the rats to drink a large supplement of water rather than saline also increased blood pressure significantly to the same extent.…”

“…This rise in blood pressure following nephrectomy has been reported previously for rats and dogs;" l2 although this finding has not been observed consistently. l3 i4 Several explanations for increases in blood pressure following nephrectomy have been suggested, including reductions in tissue compliance 15 and lack of inactivation of an extrarenal pressor mechanism in the rat. 16 It is also possible that an increase in serum osmolarity accompanied by a concomitant elevation in the circulating ADH titer may contribute to postnephrectomy blood pressure elevation; however, these measurements have not been made.…”